The 8.8 cm Flak, with a legendary reputation for anti-tank warfare, was a German anti-aircraft cannon used in the Second World War. Three versions were developed, the 8.8 cm Flak 18/36/37 which came into use on all fronts. At times up to 11,000 guns were operational and formed the backbone of the air defences against bombing raids. The maximum vertical ceiling was 10.6 km, the range 14.8 km. They could fire about 15-20 rounds per minute.